aria-function details

All,

I came across "aria-function" being used in the COGA techniques, while I 
was trying to understand SC 1.3.6 Indentify Purpose in WCAG 2.1.

https://rawgit.com/w3c/coga/master/techniques/index.html

I'm not finding a reference to the attribute anywhere in the WAI-ARIA specs.

Is there a formal description yet, or one coming together, that details 
how aria-function should be used?

Is there support yet in any browsers/AT etc. we can use to test 
implementations?

There's also a few other unfamiliar WAI-ARIA attributes in the COGA 
draft, I'm not finding details for:

  * aria-feedback
  * aria-explain
  * aria-numberfree

Assistance much appreciated...

greg